The formula

(frequency) = (speed of light) / (wavelength)

says that the speed of light is constant as per Einstein

if and only if

ANY frequency shift entails (is caused by) an inversely proportional wavelength shift.

The consequent, "any frequency shift entails (is caused by) an inversely proportional wavelength shift", is obviously false, even absurd:

Doppler effect - when an observer moves toward a stationary source https://www.youtube.com/watch?v=bg7O4rtlwEE

"Thus, the moving observer sees a wave possessing the same wavelength [...] but a different frequency [...] to that seen by the stationary observer." http://farside.ph.utexas.edu/teachin...ml/node41.html

Accordingly, the antecedent, "the speed of light is constant as per Einstein", is false as well.

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